The present invention relates generally to aircraft and more particularly to flight control surface actuation systems.
Power Control Units (PCU) are used to apply loads for positioning and maintaining the position of aircraft flight control surfaces such as ailerons, elevators, rudders, spoilers, etc. Conventional PCUs are typically sized for stall load and a required rate. The required rate typically involves low loads, either a no-load condition, a low-load condition, or a maximum allowable time to travel from surface faired to a specified surface position under specific flight conditions. For simplicity, subsequent discussions herein shall assume a no-load rate requirement. Stall load is referred to as the maximum amount of force that the PCU actuator can exert. The maximum no-load rate refers to the fastest rate at which an actuator piston can move when the control valve is wide open and no load is on the actuator.
Sizing a PCU according to a stall load and a required rate leads to inefficiencies due to flight dynamics. That is, conventional PCUs are relatively inefficient in terms of the required horsepower and hydraulic system weight under high rate and low load conditions (e.g., near xe2x80x9caerodynamic neutralxe2x80x9d or no load for the flight control surface). The term xe2x80x9caerodynamic neutralxe2x80x9d refers to the position of the flight control surface at which the net air load on the surface is zero such as when the pressure below a horizontally-oriented flight control surface is equal to the pressure above the surface.
Accordingly, a need exists for a flight control surface actuation system and method that is highly efficient and well suited for use with the present day commercial aircraft. The system should substantially reduce the hydraulic fluid flow and horsepower required to provide sufficient actuation power to meet the actuation requirements during normal and emergency flight conditions of the aircraft. Ideally, the system should provide a stall load and a maximum no-load rate that are at least comparable (i.e., substantially identical) with conventional PCUs.
In one preferred form, the present invention provides an apparatus for providing actuation power to an aircraft flight control surface. The apparatus includes a first actuator and a second actuator, where the second actuator has a bypass mode and an assist mode. The mode of the second actuator is based upon the internal differential pressure across the first actuator. The apparatus further includes a mode select valve for selecting between the bypass mode and the assist mode for the second actuator, and a solenoid valve that when energized causes the mode select valve to select the other mode for the second actuator. When the second actuator is in the bypass mode, the first actuator provides the actuation power for the aircraft flight control surface. But, when the second actuator is in the assist mode, both the first and second actuators provide the actuation power for the aircraft flight control surface. Accordingly, the apparatus allows the flight control surface to be operated in a more efficient manner with less hydraulic flow being required.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating at least one preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.